BR112019017881B1 - MULTI-LAYER FILM, PACKAGING AND MULTI-LAYER STRUCTURE - Google Patents

Abstract

The present invention provides multilayer films and packages formed from such films. In one aspect, a multilayer film comprises Layer A which is a sealing layer having an upper face surface and a lower face surface and comprising at least 30 weight percent low density polyethylene based on the weight of Layer A; and Layer B having an upper face surface and a lower face surface and comprises at least 70 percent by weight of at least one homopolymer polypropylene, random copolymer polypropylene, an impact polypropylene copolymer, or a combination thereof based on the weight of Layer B, wherein the upper face surface of Layer B is in adherent contact with a lower face surface of Layer A, wherein the film is configured to provide a peelable seal that opens due to delamination between Layer A and Layer B.

Description

Field

[001] The present invention relates to multilayer films and packages comprising such films.

Introduction

[002] Heat-sealable and easy-to-open films are used on a large scale to temporarily close containers that include, for example, food products. For example, the peelable film can seal to a rigid container such as a tray. During use, a consumer removes the tear-off film.

[003] The thermoadhesive films need to be able to perform sealing through the application of heat. During typical sealing processes, the backing layer or mantle layer comes into direct contact with a heated surface, such as a sealing jaw. Heat is thus transferred through the backing layer of the film to melt the inner sealing layer to form a seal.

[004] The force required to pull apart a seal is called “seal strength” or “heat seal strength”, which can be measured in accordance with ASTM F2029-00(B). Desired seal strength will vary based on specific end-user applications. For flexible packaging applications, such as cereal liners, snack boxes, cracker tubes, and cake mix liners, the desired seal strength is generally in the range of about 2 to 10 N/15 mm. For example, for pop-open cereal box liners, a seal strength in the range of about 3 to 6 N/15 mm is commonly specified, although specific targets will vary based on individual manufacturing requirements. In addition to flexible packaging application, a resealable, peelable film can also be used in rigid packaging applications such as lids for convenience items (eg snacks such as puddings) and medical devices. Typical rigid packages also have a seal strength of about 3 to 6 N/15 mm.

[005] Films or multilayer structures to be sealed usually include a sealing layer that when heated seals the film or structure to another film surface (of the same film or a different film), to a rigid package, or to another surface. There are numerous peeling systems by which a package can be opened.

[006] In an adhesive peeling system, a film or a multilayer structure with a sealing layer is sealed to a substrate (for example, another film or other multilayer structure, a rigid package, etc.). If the substrate does not include a sealing layer, the sealing layer separates from the substrate (eg, the film or multi-layer structure with the sealing layer is cleanly removed from the substrate). If the substrate also includes a sealant layer, there will be a clear separation between the sealant layers.

[007] In a cohesive peeling system, the seal opens cohesively within the sealant layer. In such a system, the residual sealant layer can be visible on the substrate when the failure occurs within the sealant layer.

[008] In a tear or delamination peel system, the seal remains tight, but the sealant layer adhesively delaminates from the substrate.

[009] Additional information on such systems can be found in Technical Bulletin No. 106/2011, “Guideline for the design of 'easy opening' peelable packaging systems”, published by the Industrial Association for Food Technology and Packaging (June 2011), which is hereby incorporated by reference.

[0010] Burst stripping opening mechanisms may be particularly desirable for some applications.

[0011] There remains a need for new approaches to films and/or multilayer structures that provide consistent and more easily customizable opening forces when incorporated into a package.

summary

[0012] The present invention provides multilayer films that can provide consistent and customizable opening forces when incorporated into a package. For example, in some embodiments, multilayer films, when incorporated into a package, can open by delamination within the multilayer film (i.e., tear peeling). In some embodiments, for example, the multilayer film provides a peelable seal that opens due to delamination between a sealing layer and an adjacent layer. Multilayer films, in some embodiments, can provide an "easy open" seal (for example, the film can have a maximum seal strength of 2.5 to 6.5 N/15 mm at temperatures between 100°C and 140° C when measured in accordance with ASTM F2029-00(B)).

[0013] In one aspect, the present invention provides a multilayer film comprising Layer A which is a sealing layer having an upper face surface and a lower face surface and comprises at least 30 weight percent low density polyethylene based on Tier A weight; and Layer B having an upper face surface and a lower face surface and comprising at least 70 percent by weight of at least one homopolymer polypropylene, random copolymer polypropylene, an impact polypropylene copolymer, or a combination thereof based on the weight of Layer B, wherein the upper face surface of Layer B is in adherent contact with a lower face surface of Layer A, wherein the film is configured to provide a peelable seal that opens due to delamination between Layer A and Layer B.

[0014] In another aspect, the present invention relates to a package, such as a pouch, comprising any one of the multilayer films disclosed herein.

[0015] In another aspect, the present invention relates to a package comprising any one of the multilayer films disclosed herein and a tray, wherein the upper face surface of layer A is sealed with respect to at least a portion of the tray.

[0016] In another aspect, the present invention relates to a multilayer structure comprising any of the multilayer films disclosed herein laminated to a substrate.

[0017] In another aspect, the present invention relates to a package comprising any of the multilayer structures disclosed herein.

[0018] In another aspect, the present invention relates to a package comprising any of the multilayer structures disclosed herein and a tray, wherein the upper face surface of layer A is sealed to at least a portion of the tray.

[0019] These and other modalities are described in greater detail in the Detailed Description.

Brief Description of the Figure

[0020] Figure 1 is a graph illustrating the heat seal strengths of multilayer films according to some embodiments of the present invention and comparative films at various temperatures.

Detailed Description

[0021] Unless otherwise indicated, it is implied from the context, or is customary in the art, that all parts and percentages are based on weight, and all test methods are current as of the date of submission of this disclosure.

[0022] The term “composition,” as used herein, refers to a mixture of materials comprising the composition, as well as the reaction products and decomposition products formed from the materials in the composition.

[0023] “Polymer” means a polymeric compound prepared by polymerizing monomers, whether of the same type or a different type. The generic term polymer thus encompasses the term homopolymer (used to refer to polymers prepared from only one type of monomer, with the understanding that trace amounts of impurities may be incorporated into the polymer structure) and the term interpolymer as defined hereinafter. Trace amounts of impurities (eg catalyst residues) may be incorporated into and/or within the polymer. A polymer can be a single polymer, a polymer blend, or a polymer blend.

[0024] The term "interpolymer", as used herein, refers to polymers prepared by polymerizing at least two different types of monomers. The generic term interpolymer thus includes copolymers (used to refer to polymers prepared from two different types of monomers) and polymers prepared from more than two different types of monomers.

[0025] The terms "olefin-based polymer" or "polyolefin", as used herein, refer to a polymer comprising, in polymerized form, a major amount of olefin monomer, for example, ethylene or propylene ( based on polymer weight) and optionally may comprise one or more comonomers.

[0026] "Polypropylene" means a polymer having more than 50% by weight of units derived from propylene monomer. The term "polypropylene" includes homopolymers of propylene, such as isotactic polypropylene, random copolymers of propylene and one or more C2,4-8α-olefins, in which propylene comprises at least 50 mole percent, and impact polypropylene copolymers .

[0027] The term "ethylene/α-olefin interpolymer", as used herein, refers to an interpolymer comprising, in polymerized form, a major amount of ethylene monomer (based on the weight of the interpolymer) and a α-olefin.

[0028] The term "ethylene/α-olefin copolymer", as used herein, refers to a copolymer comprising, in polymerized form, a major amount of ethylene monomer (based on the weight of the copolymer) and a α-olefin as the only two types of monomer.

[0029] The term "in tack contact" and similar terms mean that a face surface of one layer and a face surface of another layer are in touch contact and bond with each other.

[0030] The terms "which comprises", "which includes", "which has" and their derivatives do not exclude the presence of any additional components, steps or procedures, regardless of whether or not they are specifically disclosed. For the avoidance of doubt, all compositions claimed through the use of the term "comprising" may include any additive, adjuvant or additional compound, whether polymeric or otherwise, unless otherwise indicated. By contrast, the term “consisting essentially of” excludes from the scope of any subsequent citation any other component, step or procedure other than those not essential to operability. The term “consisting of” excludes any component, step or procedure that is not specifically outlined or listed.

[0031] "Polyethylene" or "ethylene-based polymer" means polymers comprising more than 50% by weight of units that have been derived from ethylene monomer. This includes polyethylene homopolymers or copolymers (meaning units derived from two or more comonomers). Common forms of polyethylene known in the art include Low Density Polyethylene (LDPE); Linear Low Density Polyethylene (LLDPE); Ultra Low Density Polyethylene (ULDPE); Very Low Density Polyethylene (VLDPE); One-site catalyzed Linear Low Density Polyethylene, including linear and substantially linear low density resins (m-LLDPE); Medium Density Polyethylene (MDPE); and High Density Polyethylene (HDPE). Such polyethylene materials are generally known in the art; however, the following descriptions may be helpful in understanding the differences between some of these different polyethylene resins.

[0032] The term “LDPE” may also be referred to as “high pressure ethylene polymer” or “highly branched polyethylene” and is defined to mean that the polymer is partially or fully homopolymerized or copolymerized in autoclave or tubular reactors at pressures above 100 MPa (14,500 psi) using free radical initiators such as peroxides (see, for example, US 4,599,392, which is incorporated herein by reference). LDPE resins typically have a density in the range of 0.916 to 0.935 g/cm3.

[0033] The term “LLDPE” includes both resin produced using traditional Ziegler-Natta catalyst systems and single-site catalysts, including, but not limited to, bis-metallocene catalysts (sometimes referred to as “m-LLDPE ”) and restricted geometry catalysts and includes linear, substantially linear or heterogeneous polyethylene copolymers or homopolymers. LLDPEs contain less long chain branching than LDPEs and include the substantially linear ethylene polymers which are further defined in US Patent 5,272,236, US Patent 5,278,272, US Patent 5,582,923 and US Patent 5,733,155; homogeneously branched linear ethylene polymeric compositions, such as those of US Patent 3,645,992; heterogeneously branched ethylene polymers, such as those prepared according to the process disclosed in US Patent 4,076,698; and/or blends thereof (such as those disclosed in US 3,914,342 or US 5,854,045). LLDPEs can be produced through gas phase, solution phase or slurry phase polymerization or any combination thereof, using any type of reactor or reactor configuration known in the art.

[0034] The term “MDPE” refers to polyethylenes that have densities from 0.926 to 0.935 g/cm3. "MDPE" is typically produced using chromium or Ziegler-Natta catalysts or using single-site catalysts including, but not limited to, bis-metallocene catalysts and restricted geometry catalysts and typically has a molecular weight distribution (“MWD”) greater than 2.5.

[0035] The term "HDPE" refers to polyethylenes that have densities greater than about 0.935 g/cm3 that are generally prepared with Ziegler-Natta catalysts, chromium catalysts or single-site catalysts that include, but are not limited to, catalysts of bis-metallocene and restricted geometry catalysts.

[0036] The term "ULDPE" refers to polyethylenes that have densities of 0.880 to 0.912 g/cm3, which are generally prepared with Ziegler-Natta catalysts, chromium catalysts or single-site catalysts that include, but are not limited to, catalysts of bis-metallocene and restricted geometry catalysts.

[0037] In one aspect, the present invention provides a multilayer film comprising Layer A which is a sealing layer having an upper face surface and a lower face surface and comprising at least 30 weight percent low density polyethylene (LDPE) based on Tier A weight; and Layer B having an upper face surface and a lower face surface and comprises at least 70 percent by weight of at least one homopolymer polypropylene, random copolymer polypropylene, an impact polypropylene copolymer, or a combination thereof based on the weight of Layer B, wherein the upper face surface of Layer B is in adherent contact with a lower face surface of Layer A, and where the film is configured to provide a peelable seal that opens due to delamination between Layer A and the Layer B.

[0038] In some embodiments, the multilayer film exhibits a maximum seal strength of 2.5 to 6.5 N/15 mm at temperatures between 100°C and 140°C when measured in accordance with ASTM F2029-00(B) .

[0039] In some embodiments, Layer A comprises at least 50 weight percent low density polyethylene (LDPE) based on the weight of Layer A. Layer A comprises at least 70 weight percent LDPE based on Tier A weight in some modalities. In some embodiments, Layer A comprises up to 100 weight percent LDPE based on the weight of Layer A. In some embodiments, Layer A further comprises linear low density polyethylene (LLDPE).

[0040] In some embodiments, layer B comprises at least 95 percent by weight of at least one homopolymer polypropylene, random copolymer polypropylene, impact polypropylene copolymer, or a combination thereof based on the weight of Layer B .

[0041] Multilayer films of the present invention, in some embodiments, may include one or more additional layers. For example, in some embodiments, the multilayer film may further comprise a barrier layer. In some embodiments, the multilayer film further comprises Layer C having an upper face surface and a lower face surface, wherein the upper face surface of Layer C is in adherent contact with a lower face surface of Layer B. In some of these embodiments, the Layer C comprises a polyolefin.

[0042] A multilayer film of the present invention may comprise a combination of two or more embodiments as described herein.

[0043] Some embodiments of the present invention relate to packaging, such as food packaging. In some embodiments, a package of the present invention comprises a multilayer film according to any of the embodiments disclosed herein. The packaging, in some embodiments, is a bag. In some embodiments, a package of the present invention comprises a multilayer film according to any of the embodiments disclosed herein and a tray, wherein the upper face surface of layer A is sealed to at least a portion of the tray.

[0044] Some embodiments of the present invention refer to multilayer structures. In some embodiments, a multilayer structure comprises a multilayer film according to any of the embodiments disclosed herein. The substrate, in such embodiments, comprises an oriented polyethylene terephthalate film, an oriented polypropylene film, an oriented polyamide film, aluminum or a polyethylene film. Such multilayer structures can be used to form a package, such as a food package. In some of these embodiments, a package comprises a multilayer structure according to any of the embodiments disclosed herein. In some embodiments, a package of the present invention comprises a multilayer structure according to any one of the embodiments disclosed herein and a tray, wherein the upper face surface of layer A is sealed to at least a portion of the tray.

[0045] A multilayer structure of the present invention may comprise a combination of two or more embodiments, as described herein.

[0046] A package of the present invention may comprise a combination of two or more embodiments as described herein.

Sealing Layer (Layer A)

[0047] The multilayer films of the present invention comprise a first layer (Layer A) which is a sealing layer. As set forth herein, the sealing layer comprises at least 30 percent by weight and up to 100 percent by weight low density polyethylene based on the weight of Layer A in some embodiments. While not wishing to be bound by a particular theory, it is believed that the combination of Layer A having a significant amount of a polyethylene having a high amount of long chain branching (e.g., LDPE) with Layer B (discussed further below) having at least 70 weight percent polypropylene provides a mismatch between the layers, which provides desirable peel strength due to the failure of delamination between Layer A and Layer B.

[0048] Layer A comprises a significant amount of low density polyethylene (LDPE). In some embodiments, Layer A comprises at least 30 percent by weight of LDPE, based on the weight of Layer A. Layer A, in some embodiments, comprises at least 50 percent by weight of LDPE, based on the weight of Layer A. Layer A. In some embodiments, Layer A comprises at least 70 weight percent LDPE, based on the weight of Layer A. Layer A comprises at least 90 weight percent LDPE, based on the weight of Layer A In some embodiments, Layer A comprises at least 95 weight percent LDPE, based on the weight of Layer A. Layer A comprises up to 100 weight percent LDPE, based on weight of Layer A in some embodiments . It should be understood that blends of different LDPE resins may also be included in Layer A and all references to LDPE should generally be understood to refer to one or more LDPE resins.

[0049] In some embodiments, LDPE has a density of 0.916 to 0.935 g/cm3. All individual values and subranges from 0.916 to 0.935 g/cm3 are included and disclosed here; for example, the density of the LDPE can be from 0.918 to 0.930 g/cm3 or alternatively 0.920 to 0.932 g/cm3 or alternatively 0.920 to 0.930 g/cm3.

[0050] In some embodiments, LDPE has a melt index (I 2 ) of 20 g/10 minutes or less. All individual values and subranges up to 20 g/10 minutes are included and disclosed in this document. For example, LDPE can have a lower limit melt index of 0.1, 0.2, 0.25, 0.5, 0.75, 1, 2, 4, 5, 10 or 15 g/10 minutes up to an upper limit of 1, 2, 4, 5, 10 or 15 g/10 minutes. LDPE has a melt index (I2) of up to 10 g/10 minutes in some embodiments. LDPE has a melt index (I2) of up to 5 g/10 minutes in some embodiments. In some embodiments, the LDPE has a melt index (I 2 ) of less than 3 g/10 minutes. LDPE, in some embodiments, has a melt index (I 2 ) of 0.1 to 2.5 g/10 minutes.

[0051] Examples of commercially available LDPE that can be used in embodiments of the present invention include DDOW™ LDPE 303E, DOW™ LDPE 352E and DOW™ LDPE 310E, as well as other low density polyethylenes that are commercially available from The Dow Chemical Company, as well as other commercially available low density polyethylenes from others in the industry.

[0052] As noted above, in some embodiments, Layer A may further comprise linear low density polyethylene (LLDPE). While not wishing to be bound by a particular theory, it is believed that incorporating some amount of LLDPE into Layer A helps to improve compatibility and adhesion with Layer B, which can increase the resistance to peeling between the two layers. Thus, the amount of LLDPE to be included in Layer A can vary, for example, depending on the desired peel strength.

[0053] In some embodiments where LLDPE is included in Layer A, Layer A comprises up to 70 percent by weight of LLDPE, based on the weight of Layer A. Layer A, in some embodiments, comprises up to 50 percent in weight of LLDPE, based on the weight of Layer A. In some embodiments, Layer A comprises up to 30 weight percent LLDPE, based on weight of Layer A. Layer A comprises up to 10 weight percent LLDPE, based on the weight of Layer A. In some embodiments, Layer A comprises up to 5 percent by weight of LLDPE, based on the weight of Layer A. It should be understood that blends of different LLDPE resins may also be included in Layer A , and all references to LLDPE should generally be understood to refer to one or more LLDPE resins.

[0054] The LLDPE(s) that may be used in layer A have a density less than or equal to 0.955 g/cm3 in some embodiments. All individual values and subranges less than or equal to 0.955 g/cm3 are included and disclosed herein; for example, the density of the LLDPE(s) can be up to an upper limit of 0.955, 0.950, 0.945, 0.940, 0.935, 0.930, 0.925, 0.920 or 0.915 g/cm 3 . In some aspects of the invention, the LLDPE(s) has a density greater than or equal to 0.870 g/cm3. All individual values and subranges between 0.870 and 0.955 cm3 are included and disclosed herein.

[0055] In some embodiments, LLDPE has a melt index (I 2 ) of 20 g/10 minutes or less. All individual values and subranges up to 20 g/10 minutes are included and disclosed in this document. For example, LLDPE may have a lower limit melt index of 0.1, 0.2, 0.25, 0.5, 0.75, 1, 2, 4, 5, 10 or 15 g/10 minutes up to an upper limit of 1, 2, 4, 5, 10 or 15 g/10 minutes. LLDPE has a melt index (I2) of up to 10 g/10 minutes in some embodiments. LLDPE has a melt index (I2) of up to 5 g/10 minutes in some embodiments. In some embodiments, the LLDPE has a melt index (I 2 ) of less than 3 g/10 minutes. LLDPE, in some embodiments, has a melt index (I 2 ) of 0.1 to 2.5 g/10 minutes.

[0056] Examples of commercially available LLDPE that can be used in embodiments of the present invention include DOWLEX™ 4056.01G, DOWLEX™ 2045.01G and DOWLEX™ NG 5056G, as well as other linear low density polyethylenes that are commercially available from The Dow Chemical Company , as well as other commercially available linear low density polyethylenes from others in the industry.

[0057] Instead of LLDPE, Layer A may comprise, in addition to LDPE, other polyethylene resins having similar or lower densities and similar melt indices as LLDPE, including enhanced polyethylenes and polyolefin plastomers. A non-limiting example of a commercially available intensified polyethylene that can be used in some embodiments in place of LLDPE is ELITE™ 5400G (density 0.916 g/cm3 and a melt index (I2) of 1.0 g/10 minutes ) which is commercially available from The Dow Chemical Company. A non-limiting example of a commercially available polyolefin plastomer that can be used in some embodiments in place of LLDPE is AFFINITY™ PL 1881G (density 0.904 g/cm3 and a melt index (I2) of 1.0 g/cm3). 10 minutes), which is commercially available from The Dow Chemical Company.

[0058] In some embodiments, smaller amounts (e.g., less than 5 percent by weight based on the weight of Layer A) of other polyethylenes may also be included in Layer A.

[0059] In some embodiments, the sealing layer (layer A) may be corona treated using techniques known to those skilled in the art prior to sealing the multilayer film.

Layer B

[0060] The multilayer films of the present invention include a second layer (Layer B) having an upper face surface and a lower face surface, the upper face surface of Layer B being in adherent contact with a lower face surface of the sealing layer (Layer A). Layer B comprises at least 70 percent by weight and up to 100 percent by weight polypropylene (e.g., homopolymer polypropylene, random copolymer polypropylene, an impact copolymer, or a combination thereof) based on the weight of Layer B As noted above, while not wishing to be bound by a particular theory, it is believed that the combination of the polypropylene in Layer B with Layer A having a significant amount of a polyethylene having a high amount of long chain branching (e.g., LDPE ) provides a mismatch between the layers, which provides desirable peel strength due to the delamination failure between Layer A and Layer B.

[0061] The polypropylene may comprise homopolymer polypropylene, random copolymer, impact polypropylene copolymer or a combination thereof.

[0062] A variety of homopolymer polypropylenes can be used in Layer B in various embodiments. Typically, homopolymer polypropylenes have a melt flow rate of 0.5 to 10 g/10 minutes. Examples of commercially available homopolymer polypropylene that can be used in embodiments of the present invention include INSPIRE 147 and DH357.01, as well as other homopolymer polypropylenes that are commercially available (or in the case of INSPIRE 147, previously available) from Braskem Europe GmbH.

[0063] A variety of random copolymer polypropylenes can be used in Layer B in various embodiments. With random copolymer polypropylene, ethylene is typically the other monomer included. Typically suitable random copolymer polypropylenes have a melt flow rate of 0.5 to 10 g/10 minutes. Examples of commercially available random copolymer polypropylene that can be used in embodiments of the present invention include INSPIRE 361 and DR152.00, as well as other random copolymer polypropylenes, which are commercially available from Braskem Europe GmbH.

[0064] A variety of polypropylene impact copolymers can be used in Layer B in various embodiments. The impact polypropylene copolymer is typically either an ethylene/propylene copolymer, an ethylene-butene rubber phase dispersed within a homopolypropylene, or an ethylene-butene rubber phase dispersed in the random copolymer matrix. Suitable impact polypropylene copolymers typically have a melt flow rate of 0.5 to 10 g/10 minutes. Examples of commercially available impact polypropylene copolymers that can be used in embodiments of the present invention include INSPIRE 137, INSPIRE 114 and INSPIRE 153, as well as other impact polypropylene copolymers that are commercially available from Braskem Europe GmbH.

[0065] In some embodiments, Layer B comprises at least 70 weight percent polypropylene based on the weight of Layer B. Layer B, in some embodiments, comprises at least 90 weight percent polypropylene based on weight of Layer B. Layer B comprises at least 95 weight percent polypropylene based on the weight of Layer B. In some embodiments, Layer B comprises up to 100 weight percent polypropylene based on the weight of Layer B in some embodiments. modalities. It should be understood that blends of different polypropylene resins (homopolymer polypropylene, random copolymer and/or an impact polypropylene copolymer) may also be included in Layer B and all references to polypropylene generally should be understood as referring to one or more more polypropylene resins.

[0066] In some embodiments, up to 30 percent by weight of other polyolefins, such as polyethylene and its copolymers, may also be included in Layer B.

Other Layers

[0067] Some embodiments of multilayer films of the present invention may include layers in addition to those described above. In such embodiments, which comprise three or more layers, the upper face surface of layer A would still be the upper face surface of the film. In other words, any additional layers would be in adherent contact with a lower face surface of Layer B, or another intermediate layer.

[0068] For example, a multilayer film may further comprise other layers typically included in multilayer films, depending on the application, including, for example, oxygen barrier layers, bonding layers, polyethylene layers, other polypropylene layers, etc.

[0069] As an example, in some embodiments, a multilayer film may comprise another layer (Layer C) having an upper face surface and a lower face surface, wherein the upper face surface of Layer C is in adherent contact with a face surface bottom of Layer B.

[0070] In some of these embodiments, Layer C may comprise one or more polyolefins, such as polyethylene, polypropylene, or mixtures thereof.

[0071] Layer C, in some embodiments, comprises polyethylene. In such embodiments, layer C may comprise any polyethylene known to those skilled in the art as suitable for use as a layer in a multilayer film based on the teachings presented herein. Examples of polyethylenes that can be used in Layer C include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), high density high density polyethylene melt strength (HMS-HDPE), ultra high density polyethylene (UHDPE), intensified polyethylenes and others. However, to the extent that Layer C comprises LDPE, the total amount of LDPE must comprise 30 percent or less of Layer C, based on the total weight of Layer C, in order to minimize the possibility of delamination occurring between Layer B and Tier C instead of between Tier A and Tier C.

[0072] Layer C, in some embodiments, comprises polypropylene. The polypropylene may comprise propylene/α-olefin copolymer, propylene homopolymer or mixtures thereof. The propylene/α-olefin copolymer, in various embodiments, can be random copolymer polypropylene (rcPP), impact copolymer polypropylene (hPP + at least one elastomeric impact modifier) (ICPP), high impact polypropylene (HIPP) , high melt strength polypropylene (HMS-PP), isotactic polypropylene (iPP), syndiotactic polypropylene (sPP), propylene-based copolymers with ethylene, and combinations thereof.

[0073] However, as noted above, layer C may comprise any number of other polymers or polymer blends. For example, if the multilayer films include a barrier layer, Layer C could be a tie layer in adherent contact between Layer B and the barrier layer.

[0074] Depending on the composition of the additional layer and the multilayer film, in some embodiments, the additional layer may be co-extruded with other layers in the film.

Additions

[0075] It should be understood that any of the foregoing layers may further comprise one or more additives known to those skilled in the art, such as, for example, antioxidants, ultraviolet light stabilizers, heat stabilizers, glidants, antiblockers, pigments or dyes , processing aids, crosslinking catalysts, flame retardants, nucleating agents, fillers and foaming agents.

[0076] Multilayer films comprising the combinations of layers described herein can have a variety of thicknesses depending on, for example, the number of layers, the intended use of the film, and other factors. Multilayer films of the present invention, in some embodiments, have a thickness of 25 to 200 microns (typically 35 to 150 microns).

[0077] Multilayer films of the present invention, in some embodiments, can advantageously provide desirable sealing properties. For example, the multi-layer film can have a sealing strength to provide an "easy open" package that opens through "peel off" due to delamination between Layer A (seal layer) and Layer B (the layer adjacent to the layer sealant). In some embodiments, multilayer films of the present invention exhibit a maximum seal strength of 2.5 to 6.5 N/15 mm at temperatures between 100°C and 140°C when measured in accordance with ASTM F2029-00(B).

Multilayer Film Preparation Methods

[0078] Multilayer films can be formed using techniques known to those skilled in the art based on the teachings presented herein. For example, with respect to layers that can be coextruded, those layers can be coextruded as blown films or cast films using techniques known to those skilled in the art based on the teachings described herein. In particular, based on the compositions of the different film layers disclosed herein, blown film manufacturing lines and cast film manufacturing lines can be configured to coextrude multilayer films of the present invention in a single extrusion step using techniques known in the art. skilled in the art based on the teachings of this document.

[0079] As indicated above, in some embodiments, the sealing layer (layer A) may be corona treated using techniques known to those skilled in the art based on the teachings described herein.

Multilayer Structures

[0080] Some embodiments of the present invention also refer to multilayer structures. In some embodiments, a multilayer structure comprises a multilayer film according to any of the embodiments disclosed herein laminated to a substrate. The substrate can be, for example, an oriented polyethylene terephthalate film, an oriented polypropylene film, an oriented polyamide film, aluminum foil, a polyethylene film or paper, as well as metallised and coated versions of the polymeric films (e.g. , coated with silicon dioxide, aluminum oxide, polyvinylidene chloride, ethylene vinyl acetate, polyvinyl alcohol or acrylics).

[0081] The substrate may comprise a film of polyethylene terephthalate, in some embodiments. For example, in some embodiments, the multilayer structure comprises a polyethylene terephthalate film and an upper face surface of the polyethylene terephthalate film is laminated to a lower face surface of the multilayer film. In such embodiments, any polyethylene terephthalate film known to those skilled in the art based on the teachings described herein can be used.

[0082] In some embodiments, the first film may comprise polypropylene, such as, for example, a biaxially oriented polypropylene film. For example, in some embodiments, the multilayer structure comprises a biaxially oriented polypropylene film and an upper face surface of the polypropylene film is laminated to a lower face surface of the multilayer film. In such embodiments, any biaxially oriented polypropylene film known to those skilled in the art based on the teachings described herein can be used.

[0083] Such multilayer structures can be formed by laminating a face surface of a multilayer film of the present invention to a face surface of the substrate using techniques known to those skilled in the art based on the teachings of the present invention. For example, in some embodiments, where the substrate comprises a polyethylene terephthalate film, the polyethylene terephthalate film may be laminated to a lower face surface of Layer B (or the outermost layer of the multilayer film is Layer B not is an outer layer) with an upper face surface of the sealing layer (Layer A) remaining as the upper face surface of the laminated multilayer film.

packaging

[0084] Multilayer films and multilayer structures of the present invention can be used to form packages. Such packages can be formed from any of the multilayer films and multilayer structures described herein.

[0085] Examples of such packaging may include flexible packaging, pouches, upright pouches, and pre-made packages or pouches. In some embodiments, the multilayer films of the present invention can be used for food packaging. Examples of foods that can be included in these packages include meats, cheeses, cereals, nuts, juices, sauces and others. Such packages can be formed using techniques known to those skilled in the art based on the teachings herein and based on the particular use for the package (e.g., type of food, amount of food, etc.).

[0086] Packages using multilayer films of the present invention may advantageously be formed with heat seal packaging equipment using continuously heated seal bars, in some embodiments. The thermal resistance properties of the outer layer of multilayer films help to protect the film structure during package formation with the continuously heated seal bars. Examples of such packaging equipment utilizing continuously heated sealing bars include horizontal form, fill and seal machines and vertical form, fill and seal machines. Examples of packages that can be formed from such equipment include upright pouch type pouches, 4 corner packages (pillow pouches), flap seal packages and the like.

[0087] In other embodiments, multilayer films or multilayer structures of the present invention can be sealed to a sheet or tray to form a package, such as a food package. Examples of foods that can be included in these packages include meats, cheeses and other foods.

[0088] The tray can be formed from sheets based on polyesters (such as amorphous polyethylene terephthalate, oriented polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate and polyethylene naphthalate), polypropylene, polyethylene and polystyrene. Such sheets, when not polyethylene based, will typically include a heat seal layer (and possibly other layers) polyethylene based which may be provided by co-extrusion, lamination or coating. The multilayer films or multilayer structures of the present invention may be particularly well suited for use with trays or sheets formed of polyethylene terephthalate or amorphous polyethylene terephthalate. Such packages can be formed using techniques known to those skilled in the art based on the teachings herein and based on the particular use for the package (e.g., type of food, amount of food, etc.).

[0089] A multilayer film or a multilayer structure of the present invention can be sealed onto the sheet or tray through the sealing layer (Layer A) of the film using techniques known to those skilled in the art based on the teachings described herein.

test methods

[0090] Unless otherwise indicated, the following analytical methods are used in the descriptive aspects of the present invention:

Density

[0091] Samples for density measurement are prepared in accordance with ASTM D 1928. Polymer samples are pressed at 190 °C and 207 MPa (30,000 psi) for three minutes, and then at 21 °C and 207 MPa for one minute . Measurements are taken within one hour of pressing the sample using ASTM D792, Method B.

Fusion Index

[0092] Melt indices I2 (or I2) and I10 (or I10) are measured in accordance with ASTM D-1238 at 190 °C and at 2.16 kg and 10 kg load, respectively. Its values are reported in g/10 min. “Melt flow rate” is used for polypropylene based resins and determined in accordance with ASTM D1238 (230 °C at 2.16 kg).

Melt Flow Rate

[0093] Melt flow rates are measured according to ASTM D-1238 or ISO 1133 (230°C; 2.16 kg).

Heat Seal Resistance

[0094] Heat seal strength or seal strength is measured using ASTM F2029-00 as follows. The film sample, which can be of any thickness, is sealed to itself at different temperatures at a pressure of 0.5 Mpa (5 bar) and a 0.5 second dwell time (films thicker than 100 microns are sealed with a second residence time). Samples are conditioned for 40 hours and then cut into 15mm strips which are then pulled into an Instron Tensile Tester at a rate of 100mm/min 5 replicate test samples are measured and the average recorded .

[0095] Some embodiments of the invention will now be described in detail in the Examples below.

Examples

[0096] Numerous multilayer films are prepared as set out in Table 1. The films are 5-layer, 50 micron films having the following structure: Layer A (7.5 microns)/Layer B (10 microns)/Layer C (15 microns) micron)/Layer B (10 microns)/Layer D (7.5 microns). Multilayer films in accordance with some embodiments of the present invention are identified as Inventive Films, whereas other multilayer films are Comparative Films. Table 1

[0097] The percentages in Table 1 are percentages by weight based on the total weight of the respective layer. LLDPE1 is DOWLEX™ 2042EC a linear low density polyethylene having a density of 0.930 g/cm3 and a melt index (I2) of 1.0 g/10 minutes, commercially available from The Dow Chemical Company. LLDPE2 is DOWLEX™ 4056G a linear low density polyethylene having a density of 0.917 g/cm3 and a melt index (I2) of 1.3 g/10 minutes, commercially available from The Dow Chemical Company. LLDPE3 is DOWLEX™ 4056.01G a linear low density polyethylene having a density of 0.919 g/cm3 and a melt index (I2) of 1.3 g/10 minutes, commercially available from The Dow Chemical Company. LDPE1 is DOW™ LDPE 352E low density polyethylene having a density of 0.925 g/cm3 and a melt index (I2) of 2.0 g/10 minutes, commercially available from The Dow Chemical Company. LDPE2 is DOW™ LDPE 303E low density polyethylene having a density of 0.922 g/cm3 and a melt index (I2) of 0.3 g/10 minutes, commercially available from The Dow Chemical Company. rPP is INSPIRE 361 random copolymer polypropylene having a density of 0.900 g/cm3 and a melt flow rate of 1.75, commercially available from Braskem Europe GmbH. iPP is INSPIRE 137 impact polypropylene copolymer having a density of 0.900 g/cm3 and a melt flow rate of 0.8, commercially available from Braskem Europe GmbH. hPP is INSPIRE 147 homopolymer propylene having a density of 0.900 g/cm3 and a melt flow rate of 3.2, commercially available from Braskem Europe GmbH. EPE is ELITE™ 5960G intensified polyethylene available from The Dow Chemical Company having a density of 0.962 g/cm3 and a melt index (I2) of 0.85 g/10 minutes.

[0098] The films are manufactured through a conventional polyethylene blown film line to provide multilayer films with a weight distribution of 15% layer A / 20% layer B / 30% layer C / 20% layer B /15% Layer D. Resin extrusion melt temperatures for Layers A, B, C, and D are approximately 235-240°C, 225-230°C, 230-235°C, and 190-200° C, respectively. The die diameter of the blown film line is 60mm, the blowing ratio is 2.5, and the die gap is 1.8mm. The output rate is 10 kg/h.

[0099] The hot seal strengths of the films are measured using the technique described above at temperatures of 95, 100, 105, 110, 115, 120, 130, 140 and 150°C. The results are shown in Figure 1.

[00100] Comparative Film A (shown as “Comp1” in Figure 1) and Comparative Film B (shown as “Comp2” in Figure 1) exhibit locking seals that cannot be opened and the seal strength represents the tensile strength approximation of the film itself when failure occurs adjacent to the sealed area. Comparative Film C (shown as “Comp3” in Figure 1) exhibits partial delamination behavior during the seal test, but the required opening force is still higher than desired. Inventive Films 1-6 (shown as "Inv1" - "Inv6" in Figure 1) all show consistent delamination between the sealing layer and adjacent layer and appropriate strength for an easy-to-open package. Inventive Films 5 and 6 (“Inv5” and “Inv6” in Figure 1) show how the incorporation of LLDPE in the sealing layer increases the peel strength due to the high compatibility with the adjacent layer.

Claims (13)

1. Multilayer film comprising: - Layer A which is a sealing layer having an upper face surface and a lower face surface and comprises at least 30 weight percent low density polyethylene based on the weight of Layer A ; and - Layer B having an upper face surface and a lower face surface and comprises at least 70 percent by weight of at least one homopolymer polypropylene, random copolymer polypropylene, an impact polypropylene copolymer or a combination thereof based on weight of Layer B, wherein the upper face surface of Layer B is in adherent contact with a lower face surface of Layer A, the film being configured to provide a peelable seal that opens due to delamination between Layer A and the Layer B. 2. Multilayer film according to claim 1, characterized in that the film exhibits a maximum sealing strength of 2.5 to 6.5 N/15 mm at temperatures between 100°C and 140°C when measured according to with ASTM F2029-00(B). 3. Multilayer film according to claim 1 or 2, characterized in that Layer A comprises at least 50 percent by weight of low density polyethylene based on the weight of Layer A. 4. Multilayer film, according to any one of claims 1 to 3, characterized in that layer A further comprises linear low-density polyethylene. 5. Multilayer film according to any one of claims 1 to 4, characterized in that layer B comprises at least 95 percent by weight of at least one homopolymer polypropylene, random copolymer polypropylene, a polypropylene copolymer of impact, or a combination thereof based on the weight of Layer B. 6. Multilayer film, according to any of claims 1 to 5, characterized in that it further comprises Layer C having an upper face surface and a lower face surface, and the upper face surface of Layer C is in adherent contact with an inferior facial surface of Layer B. 7. Multilayer film, according to claim 6, characterized in that layer C comprises a polyolefin. 8. Multilayer film, according to any one of claims 1 to 7, characterized in that it further comprises a barrier layer. 9. Packaging, characterized in that it comprises the multilayer film as defined in any one of claims 1 to 8. 10. Packaging, according to claim 9, characterized in that the packaging is a bag. 11. Packaging according to claim 9, characterized in that it further comprises a tray, and the upper face surface of layer A is sealed to at least a portion of the tray. 12. Multilayer structure, characterized in that it comprises the multilayer film, as defined in any one of claims 1 to 8, laminated to a substrate, 13. Multilayer structure according to claim 12, characterized in that the substrate comprises an oriented polyethylene terephthalate film, an oriented polypropylene film, an oriented polyamide film, aluminum or a polyethylene film.

Images